Anesthetic Monitoring · article, the authors provide an overview of modern anesthetic monitoring and answer ... surgical procedure 3. Provide a smooth and rapid recovery from anesthesia/surgery

January/February 2012 Today’s Veterinary Practice 23

Noninvasive monitoring techniques in the anesthe-

tized dog and cat have been described since the

1990s.1 More recently, major advances in technol-

ogy have improved the efficiency and affordability of

equipment. These advancements, in turn, have improved

veterinarians’ and anesthetists ’abilities to detect abnor-

malities in the anesthetized patient.

Advances in anesthetic monitoring have led to a “gold

standard” approach that emphasizes:

•Appropriateclinicalevaluation

•Trainingofpersonnel

•Preanestheticevaluation

•Advancedmonitoringtechniques.

All of the above help minimize adverse side effects of

anesthesia and surgery.

Why Monitor Anesthetized Patients?Anesthetic agents coupled with invasive procedures can

cause drastic hemodynamic changes in the patient’s

cardiorespiratory system (Table 1, page 24). In addi-

tion, each patient exhibits different physiologic and

pharmacologic responses to anesthetic agents. Because

these responses are not always predictable, it is vital to

monitor each patient closely.

Prompt detection of respiratory or hemodynamic

instability allows the anesthetist time to properly diag-

nose what is happening and intervene. This, in turn,

prevents morbidity, such as cardiorespiratory collapse,

which, if otherwise untreated, can lead to mortality.

Furthermore, despite successful sophisticated surgery

or diagnostic procedures, lack of a rapid and smooth

recovery may defeat the purpose of performing them.

Saved by Monitoring (Case 1, page 25, and Case

2, page 27) describes how anesthetic monitoring made

a difference in the surgical experience of two patients.

AnestheticMonitoringYour Questions Answered

Jeff Ko, DVM, MS, Diplomate ACVA, and

Rebecca Krimins, DVM

Peer reviewed

This article is the first one in a series

that will discuss the goals of anesthetic

monitoring as well as associated

procedures and equipment. In this first

article, the authors provide an overview of

modern anesthetic monitoring and answer

questions about why and how to provide

cutting-edge anesthesia for your patients.

Links to AnesthesiA GuideLines

To read the American College of Veterinary

Anesthesiologists and American Animal

Hospital Association anesthesia guidelines,

go to acva.org/docs/small_Animal_

Monitoring_2009.doc and aahanet.

org/Publicdocuments/Anesthesia_

Guidelines_for_dogs_and_Cats.pdf,

respectively.

http://acva.org/docs/small_Animal_Monitoring_2009.doc

http://acva.org/docs/small_Animal_Monitoring_2009.doc

http://aahanet.org/PublicDocuments/Anesthesia_Guidelines_for_Dogs_and_Cats.pdf

http://aahanet.org/PublicDocuments/Anesthesia_Guidelines_for_Dogs_and_Cats.pdf

| ANesTHeTiC MoNiToriNg: Your QuesTioNs ANswered

Today’s Veterinary Practice January/February 201224

What information is obtained during Anesthetic Monitoring?By monitoring the anesthetized patient, the

anesthetist obtains information in the follow-

ing areas:

1. Physiologic condition of the patient (eg,

cardiovascular, respiratory, and metabolic

systems)

2. Patient’s response to anesthesia, includ-

ing anesthetic depth and level of analgesia.

In addition, assessing the status of anesthetic

equipment ensures its proper function, helping

the anesthetist prevent iatrogenic crises that

can jeopardize the patient’s health.

The information obtained via patient moni-

toring is used to achieve three goals:

1. Ensure adequate tissue perfusion with

well-oxygenated blood

2. Prevent pain before, during, and after a

surgical procedure

3. Provide a smooth and rapid recovery

from anesthesia/surgery.

Table 1. Adverse effects of Anesthetic & Analgesic drugs

Anesthetic/Analgesic drug

Common Adverse effects

Alpha-2 Adrenergic

Agonists

•dexmedetomidine•Medetomidine•Xylazine

•Bradycardia•Cardiac output reduction•Hypertension/hypotension•Vasoconstriction

Anti-inflammatory

drugs

•NsAids•steroids

•Bleeding disorder•diarrhea and vomiting•gastrointestinal ulceration•Lethargy•renal and liver failure

Benzodiazepines

•diazepam•Midazolam

•Minimal cardiorespiratory effects•Paradoxical excitement in

some patients

inhalant Anesthetic

Agents

•Halothane• isoflurane•sevoflurane

•decreased cardiac output*•decreased myocardial

contractility*•Hypothermia/hyperthermia•May result in hypotension•Vasodilation*

intravenous

induction Agents

•diazepam/ketamine•Propofol•Tiletamine/

zolazepam

•Cyanosis•occasional muscle

fasciculations and seizures•Profuse salivation/airway

secretions•respiratory depression

(hypoventilation, apnea)•Transient tachycardia•Vasodilation

Local Anesthetics

•Bupivacaine•Lidocaine•Mepivacaine

•Bradycardia•Hyperthermia in some animals;

hypothermia more likely•Cardiac arrest•Hypotension•seizure

opioids

•Buprenorphine•Butorphanol•Fentanyl•Hydromorphone•Morphine

•Bradycardia•Mydriasis/miosis•respiratory depression

(hypoventilation, apnea)•Vomiting

other sedatives

•Acepromazine•other

phenothiazine-derivatives

•Heat loss due to peripheral vasodilation†•Vasodilation and hypotension†

NSAID = nonsteroidal anti-inflammatory drug* Dose dependent † Specific for acepromazine

AnesthesiA sPeCiALty For

VeterinAry teChniCiAnsThe Academy of Veterinary technician

Anesthetists (AVtA) is a recognized specialty

of the National Association of Veterinary

Technicians in America (NAVTA). The AVTA was

officially recognized by NAVTA in January 1999,

and became its second recognized specialty;

the first being the Academy of Veterinary

emergency and Critical Care Technicians (1996).

The AVTA focuses on:

•Certifying technicians interested in

specializing in veterinary anesthesia

•enhancing members’ knowledge in the

care and management of anesthesia cases

•Providing extensive information on sources

of continuing education

•Promoting patient safety, consumer

protection, professionalism, and excellence in

anesthesia care.

Applications for the AVTA certification

examination are accepted each year. This

year’s examination will take place september

8–12, 2012, at the 18th international

Veterinary emergency & Critical Care

symposium, san Antonio, Texas. Applications

for this examination are due in January 2012.

To find out more about the AVTA, including

how to become certified, go to avta-vts.

org. A list of AVTA members, noted by the

credentials Vts (Anesthesia), can be found

on the homepage of the website.


ANesTHeTiC MoNiToriNg: Your QuesTioNs ANswered |

Saved by Monitoring

Case 1: Canine Abdominal surgery

EVAluAtion

history: A 7-year-old, 25-kg mixed-breed dog presented with a 3-month history of chronic vomiting.

Physical examination: The dog was bright and alert with strong femoral pulses; heart and lung sounds were within normal limits.

Blood Analysis: Packed cell volume, 44%; total protein, 5 g/dL; glucose, 125 mg/dL; some mild electrolyte imbalances were noted.

imaging: radiographic assessment, including a barium series, revealed dilation of the proximal small intestines.

diagnosis & treatment: intestinal foreign body was suspected and exploratory abdominal surgery was scheduled. Pre-operative fluids were administered intravenously to correct the electrolyte imbalance.

AnESthEtiC MonitoRing

Anesthetic Protocol: •Premedication with acepromazine (0.02 mg/kg iM) and hydromorphone (0.01 mg/kg iM)• induction with propofol (3 mg/kg iV)•Maintainance with isoflurane to effect

Blood Pressure Monitoring during Anesthesia: oscillometric blood pressure monitoring was performed; blood pressure values were validated with simultaneous direct blood pressure measurement via pressure transducer and an arterial catheter placed in the dorsal pedal artery.

Monitor Warning: while the dog was undergoing pre-operative surgical prepping, its blood pressure began to decrease (20 minutes after induction).

Vital Signs of Anesthetized Patient (20 Minutes After induction)

systolic blood pressure (mm Hg) 81

diastolic blood pressure (mm Hg) 32

Mean blood pressure (mm Hg) 49

Heart rate (beats/min) 110

respiratory rate (breaths/min) 9

oxygen level in blood (spo2) (%) 100

end tidal Co2 (mm Hg) 48

Temperature (°F) 100.5

diagnosis: Acepromazine/isoflurane-induced hypotension

Correction: Balanced electrolyte fluids (Plasma-Lyte A, baxter.com) were increased to 20 mL/kg/H and isoflurane reduced from 1.75% to 1.25%.

Pertinent Vital Signs After Fluid Administration & isoflurane Reduction




The new vital signs indicated improved blood pressure. intra-operatively, the dog received two additional doses of hydromorphone (for its isoflurane-sparing effect and to provide additional analgesia) to maintain isoflurane between 1.25% and 1.75%.

outcome: Foreign body material consistent with pieces of a stuffed animal was removed from the jejunum; a 4-inch section of the jejunum was resected and an anastomosis was performed. The dog recovered smoothly and uneventfully.

take-home Message: without blood pressure monitoring to guide isoflurane adjustment, analgesia management, and fluid therapy, the dog’s blood pressure would have remained low for an extensive period of time, resulting in poor tissue perfusion and potential morbidity and mortality.

don’t Miss toP 10 tiPs

ABout AnesthesiAin the November/december 2011 issue of Today’s Veterinary

Practice, our Top Ten column featured the article ten tips

to improve Anesthesia in

your Practice (page 47). dr. Lysa Posner provided information on medication combinations, local nerve blocks, decreasing induction drugs, and more. To read this article, go to our website, todaysveterinarypractice.

com, and select Back issues from the top navigation bar.

http://baxter.com



What are the target Physiologic Values for the Anesthetized dog & Cat?Physiologicandcardiorespiratoryvariablesinanesthe-

tized dogs and cats are listed in Table 2.

What are important Components of Anesthetic

Monitoring?•Pre-anesthetic Evaluation: The monitoring pro-

cess starts prior to premedication. It begins by

obtaining a complete history of the patient, fol-

lowed by a thorough physical examination, includ-

ing blood analysis and indicated diagnostics.

The patient is given an ASA (American Society of

Anesthesiologists) classification based on

assessment of its anesthetic risks (Table 3).

Deficits in homeostasis, such as dehydra-

tion, anemia, or any other significant abnor-

mality (eg, low total protein, electrolyte

imbalance, endocrine dysfunction, bleed-

ing disorders) should be stabilized prior to

any anesthetic procedure. A recent study

has shown that mortality rates are higher in

small animals with higher ASA status (ASA

III–V) regardless of anesthetic agents used.2

•Monitoring All Anesthetic Phases: Once

pre-anesthetic evaluation has been com-

pleted and the patient is approved for anes-

thesia, monitoring continues through:

» Premedication

» Induction

» Maintenance

» Recovery.

Monitoring also applies to patients that have been

prescribed take-home pain medication; this is

accomplished through follow-up phone calls with

the owner.

•Sedated Patients: Sedated patients should also be

monitored. Both the American College of Veterinary

Anesthesiologists3 (ACVA) and the American Animal

Hospital Association4 (AAHA) have monitoring

guidelines, which emphasize that a sedated patient

should receive the same quality of monitoring

care as a patient under general anesthesia. To

review these guidelines, see Links to Anesthesia

Guidelines, page 23.

Table 2. Cardiorespiratory & Physiologic Parameters in the Anesthetized dog & Cat

Variable dog Cat

Circulation Heart rate (beats per min)systolic blood pressure (mm Hg)diastolic blood pressure (mm Hg)Mean arterial blood pressure

60–120 90–14060–9070–90

120–16090–14060–9070–90

Ventilation respiratory rate (breaths per min)Tidal volume (mL/kg)Arterial blood pHPaCo2 (mm Hg)Bicarbonate (mmol/L)end-tidal Co2

8–1610–15

7.35–7.4535–4522–2635–45

12–2410–15

7.35–7.4535–4522–2635–45

oxygenation spo2 (%)Pao2 (mm Hg)

≥ 95≥ 100

≥ 95≥ 100

other Body temperature (°F)Hematocrit (%)Total protein (mg/dL)Blood glucose (mg/dL)Blood lactate (mmol/L)urine output (mL/kg/H)

98–10134–595–8.3

90–150< 21–2

98–10128–47

5.9–8.490–150

< 21–2

CO2 = carbon dioxide; PaCO2 = partial pressure of carbon dioxide in the arterial blood; PaO2 = partial pressure of oxygen in

the arterial blood; SpO2 = saturation level of oxygen in hemoglobin

Table 3. American society of Anesthesiologists Physical status Classification system

AsA Classification

Animal Health description

AsA i •Normal, healthy

AsA ii •Mild to moderate systemic disease

AsA iii •severe systemic disease, but still active

AsA iV •severe systemic disease and incapacitated

AsA V •Moribund, terminally ill

AsA-e •emergency



Saved by Monitoring

Case 2: Feline Cystolithiasis

EVAluAtion

history: A 12-year-old, 3.8-kg domestic shorthair cat presented with bladder stones.

Physical examination: The cat was alert with strong femoral pulses; heart and lung sounds were within normal limits.

Blood Analysis: Packed cell volume, 38%; total protein, 7.6 g/dL; glucose, 125 mg/dL.

imaging & diagnosis: radiographic assessment revealed multiple uroliths within the bladder.

treatment: Cystotomy was scheduled for bladder stone removal.

AnESthEtiC MonitoRing

Anesthetic Protocol: •Premedication with midazolam (0.4 mg/kg iM) and hydromorphone (0.1 mg/kg iM)• induction with propofol (3 mg/kg iV)•Maintenance with isoflurane to effect

Blood Pressure Monitoring during Anesthesia: oscillometric blood pressure monitoring was performed.

Monitor Warning: while the cat underwent surgical preparation, its blood pressure and heart rate decreased (10 minutes after induction).

Vital Signs of Anesthetized Patient

(ten Minutes After induction)





respiratory rate (breaths/min) 16

oxygen level in blood (spo2) (%) 100

end tidal Co2 (mm Hg) 38

Temperature (°F) 100.3

diagnosis: isoflurane-induced hypotension and hydromorphone-induced bradycardia

Correction:

•Balanced electrolyte fluids (Plasma-Lyte A, baxter.com) were maintained at 10 mL/kg/H.•The isoflurance percentage was already low (1.25%); lowering it any further may have allowed the cat to

awake prematurely. •An anticholinergic, glycopyrrolate (0.005 mg/kg, iV titration), was administered until the targeted heart

rate was reached (normal parameter, 120–160 beats/min) and blood pressure improved (mean blood pressure, 70–90 mm Hg).

Pertinent Vital Signs

(three Minutes after glycopyrrolate Administration)





take-home Message: Monitoring both heart rate and blood pressure simultaneously provided a useful tool to pharmacologically manipulate the heart rate in order to maintain proper blood pressure in this cat.

http://baxter.com



•Personnel: There is no single piece of monitoring

equipment that can replace the role of a capable

and vigilant anesthetist monitoring an anesthe-

tized patient. The ACVA monitoring guidelines rec-

ommend trained personnel be present for continu-

ous evaluation of a sedated/anesthetized patient. See

Anesthesia Specialty for Veterinary Technicians

(page 24) for information on technician certification

in veterinary anesthesia.

•Documentation: When a patient is under general

anesthesia, all vital signs must be evaluated and

recorded on an anesthetic record at least once every

3 to 5 minutes. The anesthetic record becomes part of

the patient’s medical record and legal documentation.

Table 4. Assessing Vital signs of sedated/Anesthetized Patients

Clinical evaluation specific Variables

Circulation •Palpation of peripheral pulses•Auscultation of heart beats using a regular

stethoscope, doppler, or esophageal stethoscope

Presence, absence, strength; frequency of heart beats with simultaneous peripheral pulses

•Assessment of capillary refill time (CrT) Prolonged CrT (> 2–3 seconds) suggests poor tissue perfusion or dehydration

Ventilation •observation of chest wall movements•excursion of rebreathing–reservoir bag•Auscultation of lung sounds•Fogging of endotracheal tube or face mask

Presence, absence, regularity, frequency, characteristics, pattern, and depth of respiration

oxygenation •Assessment of mucous membrane and tongue color

Pink (adequate oxygenation) versus pale and/or cyanotic blue color (inadequate oxygenation)

depth of

Anesthesia

Assessment of:•Palpebral, corneal, and swallowing reflexes•eyeball position•Jaw tone•Muscle and anal tone•response to noxious or surgical stimulation•Purposeful movements

Light anesthesia:

•strong palpebral and corneal reflex •Central eye position•swallowing, muscle twitching, and

purposeful movements• increase in heart and respiratory rate with/

without vocalization

Moderate anesthesia:

•Ventral rotation of the eyeball•Loss of palpebral reflex with sluggish corneal

reflex

deep anesthesia:

•Muscle relaxation and loss of jaw tone•Central eye position•No corneal reflex•No response to surgical stimulation •slow heart and respiratory rate, weak pulses

Postoperative

Pain

•observation of animal’s behavior and cardiorespiratory variables during early recovery (first hour after extubation)•use of pain scales to provide consistent pain

assessments over time•Assessment of the degree of pain and

differentiation of it from residual sedation or silent pain•differentiation between delirium,* dysphoria,†

and pain

•Vocalizing, thrashing, salivation, vomiting•Frequent changes in body position•self-mutilation•Aggression toward personnel (ie, when

palpating surgical site)• increases in heart rate and/or blood pressure•Changes in respiratory rate, pattern, or effort

CRT = capillary refill time;

*Delirium: sudden, severe confusion and rapid changes in brain function; †Dysphoria: an emotional state marked by anxiety, depression, and restlessness

Link to PAin MAnAGeMent

GuideLinesView the AAHA/AAFP Pain Management guidelines for dogs & Cats at aahanet.org/publicdocuments/

painmanagementguidelines.pdf.

http://aahanet.org/publicdocuments/painmanagementguidelines.pdf

http://aahanet.org/publicdocuments/painmanagementguidelines.pdf



What Methods & equipment are used for

Anesthetic Monitoring?Prioritiesformonitoringananesthetizedpatient

include:

•A physical assessment (Table 4) of the

anesthetized patient by qualified person-

nel

•Appropriate vital sign monitoring (Table

5).

Adverse side effects of anesthesia are min-

imized when the anesthetist systematically

and regularly evaluates circulation, ventilation,

oxygenation, and analgesia. ■

In the next article in this series, anesthetic

monitoring equipment and the physiologic

components it measures will be discussed in-

depth.

References

1. Ko JC. Noninvasive techniques in monitoring anesthetized

patients. Vet Tech 1996; 17(5):301-307.

2. Bille C, Auvigne v, Libermann S, et al. risk of anesthetic

mortality in dogs and cats: An observational cohort study of

3546 cases. Vet Anesth Analg 2012; 39:59-68.

3. American College of veterinary Anesthesiologists.

recommendations for monitoring anesthetized veterinary

patients. JAVMA 1995; 206(7):936-937.

4. American Animal Hospital Association. Anesthesia

guidelines. JAAHA 2011; 47:378-385.

Table 5. Anesthetic Monitoring equipment

Circulation

electrocardiography (eCG):

•Monitors heart rate and rhythm•definitively diagnoses arrhythmias•Monitors progress of cardiac arrhythmia treatment

ultrasonographic doppler blood flow detector:

•Measures blood flow, pulse rate, and systolic blood pressure (BP) when used with sphygmomanometer

oscillometric BP measurement:

•uses a BP cuff on the limb to obtain systolic, diastolic, and mean arterial BP at a set time interval but not continuously

invasive BP measurement:

•uses arterial catheter, BP transducer, and monitor to obtain continuous beat-to-beat pulse waves•gold standard for measuring systolic, diastolic, and

mean BP

Ventilation

respirometer:

•Measures respiratory rate and tidal volume (minute volume)

Arterial or venous blood gas:

•Measures partial pressure of Co2 (PaCo2 or PvCo2)

Capnography:

•Noninvasively measures end-tidal Co2 concentration

oxygenation

Pulse oximetry:

•Noninvasively measures saturation of oxygen in hemoglobin (spo2)

Arterial blood gas:

•Measures partial pressure of oxygen (Pao2) in arterial blood samples

Body temperature

rectal thermometer

esophageal temperature probe

infrared thermometer:

•Measures tympanic membrane temperature

depth of Anesthesia

Gas analyzer:

•Measures expiratory inhalant concentration (allows anesthetist to estimate depth of anesthesia together with other vital variables mentioned in this table)

Bispectral index (Bis) monitor:

•Algorithmic analysis of a patient’s electroencephalogram during general anesthesia

BIS = bispectral index; BP = blood pressure; CO2 = carbon dioxide;

ECG = electrocardiography; PaCO2 = partial pressure of carbon

dioxide in arterial blood; PaO2 = partial pressure of oxygen in arterial

blood; PvCO2 = partial pressure of carbon dioxide in venous blood;

SpO2 = saturation level of oxygen in hemoglobin

Jeff Ko, DVM, MS,

Diplomate ACVA,

is a professor in

the Department

of Veterinary

Clinical Sciences

at Purdue

University College

of Veterinary

Medicine. He has

authored numerous articles and book

chapters in the field of anesthesia and

pain management. Dr. Ko lectures

extensively at regional, national, and

international conferences. Dr. Ko can

be reached at [email protected].

Rebecca

Krimins, DVM, is

currently a third-

year anesthesia

resident in the

Department of

Veterinary Clinical

Sciences at

Purdue University

College of

Veterinary Medicine. Dr. Krimins is a

graduate of Ross University School of

Veterinary Medicine.

mailto:[email protected]